Monitoring and control of slurry processes for polymerizing olefins

ABSTRACT

Processes, methods and apparatus relating to olefin polymerization include the use of Raman spectrometry to monitor the concentration of reactants, products or other chemical components. One or more polymerizaton conditions are adjusted in response to those monitored concentrations. The present processes, methods and apparatus are applicable with slurry olefin polymerization process, even though such slurry processes contain solid particles were are known to interfere with Raman spectrometry. Furthermore, the present processes, methods and apparatus are applicable where there is some degree of overlap between Raman spectral peaks. Methods of monitoring and controlling olefin polymerization processes, reactants and other components use Raman spectrometry. Apparatus for olefin polymerization reactions have polymerization equipment, at least one Raman probe located in the polymerization equipment, and Raman spectrometry equipment located outside the polymerization equipment and operatively connected to at least one Raman probe.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable.

FIELD OF THE INVENTION

[0003] This invention relates to the use of Raman spectrometry inprocesses for polymerizing olefins and in methods of monitoring andcontrolling olefin polymerization processes, reactants and othercomponents. More particularly, a Raman fiber optic probe may be placedin an olefin polymerization reactor, or before or after such a reactor,for Raman spectrometry analysis. The present processes and apparatus mayemploy low resolution Raman spectrometry and measurement of liquid phaseand/or gas phase components of an olefin polymerization process. Thepresent processes and apparatus allow for quantitatively monitoring theolefin polymerization process in situ and constitute an improvement overgas chromatographic analysis conventionally employed in monitoringolefin polymerization reactions.

BACKGROUND OF THE INVENTION

[0004] Olefin monomers, such as ethylene and propylene, can bepolymerized to form polyolefins. For example, ethylene or propylene maybe homopolymerized to form polyethylene and polypropylene, respectively,or they may be copolymerized together or with higher 1-olefins such as1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene and others. Processesfor manufacturing polyolefins typically employ catalyst systemscomprising one or more catalytic metal compounds, typically transitionmetals, perhaps together with a co-catalyst and/or a support such asalumina or silica. Different types of olefin polymerization processesare available. For example, olefins may be polymerized in homogeneousprocesses or in heterogeneous processes.

[0005] One type of polymerization process employs a slurry as thereaction mixture. In slurry polymerization processes, solid olefinpolymers such as polypropylene, polyethylene and copolymers, are formedunder polymerization conditions that include a slurry as the reactionmixture. The slurry comprises the solid olefin polymer particlessuspended in a liquid diluent that is inert in the polymerizationreaction and in which the polymer is insoluble under polymerizationconditions. Typically, slurry polymerization processes are conducted ina relatively high-pressure continuous reactor, such as a loop reactor.Such reactors may be operated at pressures of about 600 psi, forexample, and at temperatures of about 60 degrees C. to about 100 degreesC. In many situations, slurry polymerization processes are relativelymore commercially desirable than other polymerization processes.

[0006] In the slurry polymerization process, components such as one ormore monomers, a diluent, and a catalyst system and possibly otherreactants (such as, for example, comonomers or hydrogen) are introducedto the polymerization reactor to form a reaction mixture. The reactionmixture is maintained under polymerization conditions for formation ofpolyolefin. After a suitable period, the slurry or a portion thereof isdischarged from the reactor through a product take-off line into asettling leg. The solid polyolefin settles out from the slurry, leavinga clear liquid comprising diluent and reactants such as the monomer. Theclear liquid and solid polyolefin then may then re-mix as they aretransferred to one or more separation chambers or flash tanks where, forexample, they are flashed to a low pressure such as about 15 or 20 psi.Some slurry loop polymerization equipment includes both a high pressureflash tank and a low pressure flash tank. Further information anddetails of slurry polymerization processes and loop reactors, includingexamples of suitable reaction conditions as well as control schemes forother important variables, such as solids concentration and productionrate, can be found in U.S. Pat. No. 3,998,995 and U.S. Pat. No.3,257,363, which are incorporated herein by reference.

[0007] It is desired to monitor and control the polymerization reactionso that one may obtain polyolefins having particular properties.Obtaining particular properties in a polyolefin may be done by controlof the component concentrations or ratios during the polymerizationprocess. Small changes in components can affect the properties of thefinal polyolefin product. Control of the concentration of olefinmonomer, and if present, comonomer and hydrogen, is required to ensurereliable finished polyolefin product properties. Other important controlparameters may include the degree of polymerization, molecular weight,or size of the polymer chain. Therefore, it is desirable to monitor theolefin polymerization process by determining monomer content and, whenone or more co-monomers are present, by determining co-monomercontent(s). It may also be desirable to determine diluent content andproduct content.

[0008] Current methods of monitoring slurry polymerization processes andthe components (reactants, products, and diluent) in such processes areless than optimal for several reasons. In loop polymerization processes,monomer and co-monomer content have typically been determined by gaschromatography (“GC”) analysis of the flash gas, that is, the gasreleased at one of the flash tanks where pressure is released. Forexample, U.S. Pat. No. 3,257,363 discloses methods of controlling thecomposition of the reaction mixture in a loop polymerization reactorwherein a gas chromatographic analyzer may be used to determine theamounts of ethylene and 1-butene reactants from a polymer-free off-gasline or with a sample stream from anywhere in the reaction system.

[0009] However, monitoring of the olefin polymerization process byanalysis of the flash gas is less than optimal for several reasons. Onereason is the amount of time for such analysis. If an analysis takes toomuch time, it generally has less value for monitoring, controlling oradjusting the olefin polymerization process. Also, another concernarises when the polymerization equipment includes more than one flashchamber, such as a high pressure flash chamber and a low pressure flashchamber. In such instances, gas chromatographic analysis of flash gastakes more time and is potentially less accurate when both high pressureand low pressure flash tanks are in operation.

[0010] While the contents of the olefin polymerization reactor may bedetermined by removing a small sample for analytical testing in a remotelaboratory, this is less favorable than monitoring in situ. It may bedangerous and difficult to remove a sample from a hot process stream,and there are risks that the sample may not be representative of theoverall reactor contents or that removing the sample may alter thesample. Sampling is time-consuming, and delay may cause the sample notto be representative of the reactor contents. A significant amount ofmaterial may be produced in the time required to remove, prepare, andanalyze a sample. The analytical data obtained from the delayed sampleis therefore of limited value for proactive process control.Furthermore, additional processing of the extracted sample may berequired yet is undesirable.

[0011] A preferred method of monitoring the polymerization process wouldmonitor the process as it happens, or as soon thereafter as practical.It is also preferable that an analysis method be performed in situ, asopposed to being performed on samples removed from the polymerizationequipment. An in situ method would reduce the need to remove samplesfrom the production environment, improve safety, and yield fastermeasurements. However, there are obstacles to providing in situ on-linechemical information in a process environment. The analytical methodmust be sufficiently accurate and precise under hostile physical andchemical conditions. The analytical method must be capable of remotedetection and analysis.

[0012] Analyses of slurry olefin polymerization processes in situ, thatis, within a slurry loop polymerization reactor or associated equipment,have been difficult if not impossible to do, since such olefinpolymerization reactions are carried out at high pressures. However,spectrophotometric apparatus such as a spectrograph and a radiationsource can be situated in a location remote from the polymerizationreactor that is to be analyzed in situ, the sampling site beingconnected to the apparatus by radiation conduits comprising fiber opticcables.

[0013] Raman spectrometry can provide qualitative and quantitativeinformation about the composition and/or molecular structure of chemicalcomponents. Raman spectrometry is based upon the vibrational energy of acompound. A sample is irradiated, preferably by a monochromatic lightsource, and the scattered light is examined through a spectrometer usingphotoelectric detection. Most of the scattered radiation has thewavelength of the source radiation, which is referred to as Rayleighscattering. However, the scattered radiation also comprises radiation atshifted wavelengths, which is referred to as Raman scattering, whichoccur at different wavelengths due to molecular vibrations. Thedifference in wavelengths between the source radiation and radiationaffected by molecular vibrations is commonly referred to as the Ramanshift. Even if monochromatic light is used as the source radiation, theRaman spectrum will comprise scattered light spread across a wavelengthband. The Raman shift or Raman spectrum conveys compositional andmolecular information regarding the component in the sample. The Ramanspectrum is extremely weak compared to the Rayleigh spectrum.

[0014] Not all substances are measurable by Raman spectrometry. Theremust be a change in polarizability during molecular vibration of asubstance in order for that substance to be Raman active.

[0015] There are several factors that have favored the use of gaschromatography as an analytical method over Raman spectrometry witholefin polymerization processes. In general, it is recognized by thosefamiliar with Raman spectrometry that the presence of solid particles ina solution to be analyzed will significantly reduce the Raman shiftobserved. In particular, slurry olefin polymerization processes includesolid polyolefin particles in the slurry. Also, the reactants andproducts in olefin polymerization processes may have peaks in theirrespective Raman spectra that are relatively close together, such aswhen ethylene is employed as a monomer and hexene is employed as aco-monomer. For example, ethylene and hexene produce similar peaks intheir Raman spectra. Ethylene exhibits a peak at 1620 cm⁻¹ while hexeneexhibits a peak at 1640 cm⁻¹. As a result, it may be difficult todistinguish between ethylene and hexene, and there is likely to be someoverlap in certain peaks. Thus, it would appear necessary to employ highresolution Raman spectrometry equipment to analyze the components ofcertain olefin polymerization processes. Furthermore, Raman spectrometryequipment, particularly high resolution Raman spectrometry equipment, isrelatively expensive, which would generally discourage its use withindustrial processes. Gas chromatography equipment has historically beenless costly than high resolution Raman spectrometry equipment.Furthermore, gas chromatography sampling systems are well established.Also, gas chromatography equipment tends to provide information that ismore readily usable, whereas Raman spectrometry equipment tends toproduce information that requires additional analysis. Engineers andoperators tend to prefer equipment that provides a relatively simplereading rather than a spectrum.

[0016] International Application No. PCT/AU86/00076, which isincorporated herein by reference, discloses monitoring the presence orconcentration of one or more chemical components by using Ramanscattering. Optical fibers are used to direct electromagnetic radiationto and from the monitored environment, so that the Raman detector may beremote from the monitored environment. It is stated that the Ramanmonitoring method is applicable to gases, liquids and solids, though noparticular chemical components are disclosed as being monitored. It isalso stated that it is necessary to examine the intensity of thescattered light at selected characteristic wavelengths. A band passfilter system is used, which has a series of narrow band passinterference filters each having a band pass between 100 cm⁻¹ and 400cm⁻¹. Each filter is chosen to give maximum transmission of the Ramanscattering of a particular component to be analyzed. This internationalapplication does not disclose the use of Raman spectrometry to monitoran olefin polymerization process, or to measure olefin monomers. Theinternational application does not disclose a method of monitoring thepresence or concentration of more than one chemical component when thosecomponents have overlapping Raman spectra or event that such monitoringis possible.

[0017] U.S. Pat. No. 5,652,653, which is incorporated herein byreference, discloses a method of on-line quantitative analysis ofchemical compositions by Raman spectrometry. The method comprisessimultaneously irradiating the monitored chemical composition and areference material. The method applies predetermined calibration meansto the standard Raman spectrum of the analyzed chemical composition toascertain the chemical composition. The method is used for analyzing apolyester manufacturing process. A polyester manufacturing processgenerally has a liquid reaction mixture that does not include solids ora slurry. The patent discloses the construction ofconstitution-intensity correlation (CIC) multivariate calibration means.This is done by comparing a plurality of peaks at different wavelengthsin the Raman spectra, which are preferably standard spectra, with aplurality of chemical compositions of known concentrations. Thewavelengths selected for construction of a CIC depend on the spectralcharacteristics of the particular component whose concentration in achemical composition is to be determined. For each component whose insitu concentration in the composition is desired to be monitored at anygiven time, a separate CIC calibration is prepared.

[0018] U.S. Pat. No. 4,620,284, which is incorporated herein byreference, relates to qualitative and quantitative analysis using Ramanscattering for substances in gaseous, liquid and solid form to providenumbers, rather than spectra, denoting the amounts of the substancespresent. It is disclosed that reference spectra are used to establish arelationship between spectra region areas and concentrations ofsubstances, and that composite reference spectra may be prepared. Thepatent discloses a hydrocarbon analyzer dedicated to “PNA” analysis as aparticular embodiment, which determines the composition of a hydrocarbonin terms of three groups: paraffins, napthlanes, and aromatics. Amongthe prior art disclosed in that patent is work accomplished using theRaman effect to analyze hydrocarbons, including an article entitled“Determination of Total Olefins and Total Aromatics.” Similarly, anarticle entitled “Low-Resolution Raman Spectroscopy,” Spectroscopy13(10) October 1998, discuss Raman spectrometric analysis of mixtures oforganic liquids as well as petroleum products.

[0019] However, it is believed that Raman spectrometry has not beenpreviously employed to monitor an olefin polymerization process.

SUMMARY OF THE INVENTION

[0020] The present processes, methods, and apparatus differ from priorprocesses and apparatus for monitoring chemical components with Ramanspectrometry in that Raman spectrometry is applied to olefinpolymerization processes. Monitoring of olefin polymerization processesby Raman spectrometry is distinguishable at least because Raman spectraof the various components may overlap, and other factors have made otheranalytical methods appear to be superior. For example, the presence ofsolid polyolefin particles in the reaction mixture of somepolymerization processes would discourage the use of Raman spectrometryfor analyzing such reaction mixtures.

[0021] A process for olefin polymerization in a slurry comprising solidpolyolefin and a diluent is provided. The process comprises the steps ofcontacting in a reaction mixture under slurry polymerization conditions:(i) at least one reactant including at least one olefin monomer andoptionally at least one comonomer and optionally hydrogen and (ii) aheterogeneous catalyst system comprising one or more catalytic metalcompounds and one or more co-catalysts; (b) making a polyolefin; and (c)monitoring the process by using Raman spectrometry equipment to providean output signal representative of one or more of reactants or thepolyolefin; and (c). The output signal is generally representative of aconcentration of either one of the reactants or the products, though thesignal that comes directly from the Raman probe will be converted to aconcentration value as described herein to provide the output signal.

[0022] The process may further comprise the step of adjusting the olefinpolymerization process in response to the output signal provided by theRaman spectrometry equipment. The olefin polymerization process can beadjusted by adjusting the concentration within the reaction mixture ofat least one chemical component with the reaction mixture.Alternatively, the olefin polymerization process can be adjusted byadjusting one or more polymerization conditions selected from the groupconsisting of polymerization temperature, polymerization pressure,withdrawal of the reaction mixture from the reactor, and circulationrate of the reaction mixture within the reactor. The Raman spectrometryequipment is operatively connected to a Raman fiber optic probe that isin contact with the reaction mixture or the polyolefin.

[0023] In some preferred embodiments, the monomer consists of ethylene.In other preferred embodiments, a comonomer is present in the reactionmixture so that it is contacted with the ethylene, and the comonomer isselected from the group consisting of 1-butene, 1-pentene,4-methyl-1-pentene, and 1-hexene.

[0024] The monitoring may be done using Raman spectrometry equipment toanalyze effluent, such as the effluent from a loop polymerizationreactor.

[0025] As another aspect, a method for monitoring and controlling anolefin polymerization reaction is provided. The method comprises (a)contacting components of a reaction mixture in a polymerization reactorunder polymerization conditions, where the components comprise amonomer, a diluent, and a catalyst system; (b) using Raman spectrometryequipment to obtain a Raman spectrum; (c) obtaining a concentration ofat least one component based upon the Raman spectrum; (d) adjusting atleast one polymerization condition in response to the concentration ofthe component. The method may also comprise obtaining a Raman spectrumof the reaction mixture, and determining the concentration of at leastone component through the use of a calibration model. In preferredembodiments, the method further comprises, prior to step (a), the stepof developing the calibration model using partial least squaresanalysis.

[0026] As yet another aspect, an apparatus for olefin polymerization isprovided. The apparatus comprises polymerization equipment comprising apolymerization reactor for slurry polymerization of one or more olefins,wherein the slurry comprises solid polymer particles and a diluent; atleast one inlet to the reactor for providing chemical components of thepolymerization; at least one outlet from the reactor for removingproduct from the polymerization reactor; at least one Raman probelocated in the polymerization equipment, where the Raman probe providesan output signal; Raman spectrometry equipment located outside thepolymerization equipment and operatively connected to at least one Ramanprobe.

[0027] The olefin polymerization apparatus may further comprises acomputer that receives a signal from Raman spectrometry equipment. Thecomputer can be operatively connected to flow control equipment foradjusting a concentration of at least one of the chemical components orthe product. Alternatively, the computer can be operatively connected toequipment for adjusting one or more of polymerization conditionsselected from the group consisting of polymerization temperature,polymerization pressure, withdrawal of the reaction mixture from thereactor, and circulation rate of the reaction mixture within thereactor. The computer may comprise a calibration model for convertingRaman spectra to at least one concentration of one or more of chemicalcomponents or of product.

[0028] The Raman probe may be a Raman fiber optic probe disposed in theoutlet or in polymerization reactor. The Raman probe can be operativelyconnected to the Raman spectrometry equipment by fiber optic cable.

[0029] In the present processes, methods and apparatus, low resolutionRaman spectrometry equipment may be used, such as, for example, Ramanspectrometry equipment having a resolution of about 15 wavenumbers toabout 30 wavenumbers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a diagram of a loop polymerization reactor comprisingRaman spectrometry equipment for monitoring a slurry olefinpolymerization process.

DETAILED DESCRIPTION OF DRAWINGS AND PREFERRED EMBODIMENTS

[0031] Some embodiments described herein are described in the terms ofthe polymerization of ethylene. However, the present processes andapparatus may be employed with any process where it is desired tomonitor and control polymerization of an olefin. It is particularlyapplicable to the operation of loop reactors which produce polyethyleneor polypropylene under slurry polymerization conditions. Polymerizationconditions generally include the concentration of reactants, productsand other chemical components, temperature, pressure, withdrawal ratefrom the reactor, and circulation rate within the reactor

[0032] A process for polymerizing olefins is provided wherein monomerand/or comonomer and/or other components may be monitored before, duringand/or after the polymerization reaction through Raman spectrometry.Such Raman spectrometry provides for improved monitoring and control ofthe process. In preferred embodiments, a Raman fiber optic probe islocated in the reactor or in a product take-off line just outside thereactor and provides an output signal from which monomer and/orcomonomer and/or diluent concentrations may be determined. The presentprocesses, methods, and apparatus provide improved process controlcompared to process control based on flash gas analysis by gaschromatography.

[0033] Raman spectrometry typically comprises providing a source ofelectromagnetic radiation, transmitting radiation to a sample,collecting scattered radiation from the sample, separating or dispersingthe energy of the scattered radiation, and detecting the radiation. Anysuitable radiation source may be employed in the present method andapparatus, preferably a radiation source having a nominal wavelength of785 nm, alternatively a radiation source having a nominal wavelength of532 nm. Various Raman spectrometry equipment, as well as underlyingprinciples, are disclosed in U.S. Pat. No. 5,652,653, which isincorporated herein by reference.

[0034] Suitable Raman analytical units include the low resolution RamanR-2000 and R-2001C, manufactured and marketed jointly by Ocean Optics,Inc. (Dunedin, Fla.) and Boston Advanced Technologies, Inc. (Marlboro,Mass.). Such low cost, low resolution Raman spectrometers have beenfound to be suitable for use in the present processes, methods andapparatus. The device consists of a solid-state diode laser with athermoelectrically cooled charge-coupled device (CCD) array miniaturedetector in the R-2001C and a computer interface card. Various other andrelated apparatus for Raman spectrometry, as well as underlyingprinciples, are disclosed in U.S. Pat. No. 5,652,653, which isincorporated herein by reference.

[0035] The laser in the R-2001C is a B&W diode laser set at 785 nm witha power of 500 mW. The fiber-optic probe has excitation and collectionfibers that use filtering to remove most of the laser line signal fromcollection. The R-2001 detector is a high-sensitivity 2048-elementlinear CCD-array configured to detect a range of signals from 200 to2800 cm⁻¹ and has a grating density of 1200 lines per mm. The detectoris thermoelectrically cooled to a constant temperature of 7° C. Thecooling allows for a better signal, and the constant temperatureprevents having to retake dark currents to avoid floating baselines,making it ideal for longer data collection periods. The R-2001 hostsoftware that comes with the spectrometer makes the data available tothe user. Spectral resolution for such a spectrometer is about 15 cm⁻¹,which places it in the category of low resolution Raman spectrometryequipment.

[0036] Preferably, a Raman fiber optic probe is employed in the presentprocesses, methods and apparatus. Suitable probes include theInPhotonics RP-785-01-05-SMA probe and the InPhotonics RP-785-100-01-SMAprobe. The InPhotonics probe is preferred for analysis where there aresolids present such as in the slurry olefin polymerization reactor. Ithas been found that other Raman fiber optic probes are not presentlyoperable in a slurry olefin polymerization reactor. have been Anothersupplier of Raman fiber optic probes is Kaiser Optical Systems, Inc.,which is similar to the InPhotonics probe in good performance inrejecting back scattering radiation. In general, a suitable Raman fiberoptic probe may be constructed by soldering metal coated, fused silicafiber optic cables into a protective metal sheath. This probe designprovides a simple, reliable method of optically sampling and remotelymonitoring a chemical composition in a harsh physical environment of amanufacturing process. It may be advisable to position optical filtersnear the sample to remove background-inducing radiation caused by thefused silica core of the fiber optic cable.

[0037] Fiber optic probes have been used to provide a means fortransmitting radiation towards a sample and collecting the scatteredradiation. Such probes may be constructed with combinations of fiberoptics, lenses, and/or mirrors. In one construction, two or more fiberoptic lines are secured closely together on the sample end. One or moreof these fiber optic lines (typically, one) are used to transmit theradiation into the sample, and one or more additional fiber optic lines(typically, more than one) are used to collect and transmit thescattered radiation back to a detector.

[0038] Thus, the same Raman probe may emit radiation and then detect theRaman scattered radiation. Radiation such as laser light may come outone part (for example, one fiber optic cable) of the Raman probe and isfocused into the sample to be measured. When the radiation contacts themolecules in the sample, it excites those molecules to a virtual state,which is a higher vibration energy level. When that molecule relaxes andcomes back to its ground state, it scatters radiation in all directions.Some of the scattered radiation returns to the Raman probe, where it isgathered by another part (for example, other fiber optic cables) of theRaman probe and fed to the detector. Some of the scattered radiationthat returns to the Raman probe reflects the molecular vibrations of thedifferent molecules in the sample. The molecule emits a photon at thevibrational energy at which the molecule is vibrating when it wascontacted by the radiation. The various molecules and vibrationalenergies scatter radiation of different energy levels, which havewavelengths, thereby forming a spectrum.

[0039] After the scattered radiation has been collected and transmitted,it is separated using a dispersion element. The dispersion element,which is typically included along with focusing and collimating opticalelements in a spectrograph, facilitates the separation of various energylevels of the scattered radiation from one another.

[0040] Raman spectrometry has previously been used as the basis for anon-line analytical method, as disclosed in U.S. Pat. No. 5,652,653. Thepresent processes, methods, and apparatus differ from the disclosure ofthat patent at least in that the present processes and apparatus do notemploy simultaneously irradiation of a reference material.

[0041] The present processes, methods and apparatus are particularlyuseful for in situ monitoring of an olefin polymerization process. Inthe present methods, both liquid phase and gas phase concentrations maybe determined by Raman analysis, while this was not readily done byother techniques. Generally, separate Raman probes will be positioned inthe gas phase and the liquid phase. The use of results of liquid phaseand gas phase analyses may provide faster and more accurate results thanfrom current gas chromatographic analyses of flash gas.

[0042] Alternatively, monitoring of the olefin polymerization processmay be accomplished by conducting Raman spectrometry at several pointsor times before, during and/or after the polymerization process, therebyproviding a method of monitoring the polymerization reaction as itproceeds. For example, one might measure the concentrations of monomer,comonomer, hydrogen, and/or other reactants or diluents as they go intoa polymerization reactor, and/or into a diluent such as isobutane,and/or in the flash gas.

[0043] As another alternative, the present processes and methods may beused to control two or more reactors in series. For example, theeffluent from effluent from an upstream reactor may be provided as inputto a downstream reactor for additional polymerization of the effluent.However, it may be desirable to supply an additional amount of monomerand/or comonomer to the second or other later reactor (a reactor otherthan the first reactor in series), and that amount can only bedetermined by rapid analysis of the components of the input. Whenreactors are connected in series, a monitoring step may includedetermining a concentration of the monomer in the effluent of theupstream reactor by Raman spectrometry equipment, and an adjusting stepmay include providing an amount of monomer or comonomer in addition tothe effluent to the downstream reactor.

[0044] By using the present process with reactors in series, one can getmore desirable properties in the product, including polyolefins having adesired bimodal or multimodal molecular weight distribution and/orhaving a comonomer selectively incorporated into the polyolefin at thehigh end of the molecular weight distribution. Additionally, residualmonomer in the effluent may be polymerized into product, therebyincreasing the efficiency of the process.

[0045] Referring to FIG. 1, there is illustrated a loop polymerizationreactor 11 and associated equipment for the polymerization process. Thisloop polymerization reactor provides a continuous path of circulation ofthe reaction slurry or reaction mixture. In this embodiment, the loopreactor 11 is jacketed by heat exchange sections 12 which are connectedby line 13 and contain a heat exchange medium supplied by line 14 andremoved by line 16 for maintaining the loop reactor 11 at a desirabletemperature. The reactor 11 is provided with suitable agitation orcirculating equipment, such as a propeller or stirrer 18 driven by amotor 17. In this type of reactor, the reaction mixture is circulatedthrough the reactor at a velocity that provides highly turbulent flow,for example, about 21 feet/second. The reaction effluent from thereactor 11 is withdrawn through a product take-off line 19 and passed toa settling leg 24 which can be a drain or vertical leg. In preferredembodiments, the reaction effluent is a slurry made up of polyethylene,unreacted ethylene, unreacted comonomer, and isobutane, and the catalystis generally contained in the polyethylene. A suitable apparatus forcontrolling the removal of polymerization reaction effluent is disclosedin U.S. Pat. No. 5,565,174, which is incorporated herein by reference.The withdrawal of effluent is regulated by suitable equipment, such as aflow rate control valve 21, pressure regulator controller 22, andpressure sensor and transmitter 23, such withdrawal equipment beingdependent upon reactor pressure.

[0046] Withdrawal of the reaction mixture may be continuous orintermittent. In the case of continuous withdrawal, changes involumetric reactor input causes changes in valve opening in the productconduit 19 to maintain constant reactor pressure. In the case ofintermittent withdrawal, changes in volumetric reactor input causeschanges in the time interval between valve openings to maintain constantreactor pressure. Some of the reactant, diluent, and catalyst arewithdrawn along with product.

[0047] The reactor effluent is passed through line 24 to a suitableproduct separator, such as a flash tank 26. The pressure of the reactoreffluent is lowered in the flash tanks. Preferably, two or more flashtanks are employed in series, because using more than one flash tank mayprovide better recovery of polyolefin. In flash tank(s) 26, thepolyolefin product is separated from the reaction effluent and passedthrough line 27 to suitable finishing equipment, such as dryers. Thevaporized components of the reaction mixture comprising unreactedreactants and diluent are withdrawn through line 28 from flash tank 26and passed to a suitable cyclone chamber 29 to ensure removal ofpolyolefin fines, which are withdrawn through line 31. Thepolyolefin-free vapors are then passed by line 32 to other separationequipment (indicated by the break in line 32) to further separatereactant from diluent, which is compressed by compressor 33 and recycledback to the reaction system by line 34 with the olefin feed. Recycleline 34 can be provided with the usual flow control equipment, such asflow rate control valve 36, flow rate controller 37, and differentialpressure transmitter 38.

[0048] In the embodiment shown in FIG. 1, a monomer such as ethylene orpropylene is supplied from conduit 41, which may have flow controlapparatus such as the flow rate control valve 42, flow rate controller43, and differential pressure transmitter 44. A comonomer may beprovided from conduit 45, and the flow rate of comonomer may beregulated by flow control apparatus such as flow rate control valve 46,flow rate controller 47, and differential pressure transmitter 48. Adiluent, such as isobutane, pentane, isopentane, mixtures thereof, orother suitable paraffins having 3 to 12 and preferably 3 to 8 carbonatoms per molecule, is supplied through conduit 49, and its flow ratemay be regulated by flow control apparatus such as flow rate controlvalve 51, flow rate controller 52, and differential pressure transmitter53. The diluent may be provided to reactor 11 directly by line 50 and/orindirectly through the catalyst feed system described below. The monomerand comonomer feeds can be combined and passed by a common olefin feedstream 54 to reactor 11. The mixture of olefin reactants in line 54 isestablished at a substantially constant pressure, for example 600 psi,by a pressure control valve 55.

[0049] A catalyst system, such as chromium oxide on silica or asilica-titanium catalyst, is provided from conduit 58 and introduced toreactor 11 after mixing with some diluent from line 59 in catalyst tank57. Any catalyst system suitable for polymerizing olefins may beemployed with the present processes and apparatus. In slurrypolymerization processes, it is particularly preferred to employheterogeneous catalyst systems comprising one or more catalytic metalcompounds, and co-catalysts such as an alkylaluminum or aluminoxane,perhaps with a support material such as silica. In FIG. 1, the catalystflow rate is regulated by flow control apparatus such as a suitablerotary valve 61 driven by a motor 62, which is controlled by speed ratecontroller 63. The concentration of catalyst in the reaction mixture canvary widely, particularly depending on the type of catalyst used,however, it will generally comprise 0.001 to 5 percent by weight basedon the liquid hydrocarbon diluent. The catalyst injection rate can becontrolled by means of a heat balance computer or other means tomaintain a constant rate of polymer production.

[0050] The reaction mixture circulates in the loop, where monomercontacts catalyst under suitable polymerizations conditions. As a resultof contacting monomer (and comonomer, when present) with the catalystunder such conditions, a polymerization Is reaction takes place and apolyolefin is formed. The polyolefin generally forms as solid particlesin the reaction mixture. The solid polyolefin particles in the liquiddiluent form a slurry.

[0051] The polymerization reaction, or one or more its components orconditions, may be monitored. The monitoring equipment shown in FIG. 1includes a Raman probe 66, which for clarity is shown as a boxsurrounding the loop reactor 11 but which is typically disposed mostlyor entirely within the reactor 11. The Raman probe 66 provides an outputsignal which is representative of the Raman spectrum of the chemicalcomponents in reactor 11 or some portion of those components. The outputsignal from Raman probe 66 is provided to an analyzer 68 which in turnprovides a signal to computer 67. Information transmittal paths andsignal paths are shown in FIG. 1 by dashed lines. The physical form ofthose paths may vary. In computer 67, the Raman spectrum is monitored,and the polymerization process may be controlled manually orautomatically in response to the spectrum. For example, computer 67 maysend a signal (represented in FIG. 1 by dashed lines) to one or more ofcontrollers 60, 65, 75 to adjust the amounts of reactants or diluentadded to the loop reactor or the amount of material withdrawn.Alternatively, computer 67 may send a signal to one or more of motor 17(to adjust the circulation of reaction mixture), pressure regulatorcontroller 22 (to control the withdrawal of product), or valve 61 (tocontrol the amount of catalyst provided to reactor 11).

[0052] The Raman spectrum may be used to determine the concentrations ofthe chemical components in the reactor, and/or before or after thereactor. The Raman spectrum may be used to determine the concentrationof polyolefins such as polyethylene and polypropylene, reactants such asethylene monomer and hydrogen, and diluents such as isobutane.

[0053] The peaks of the Raman spectra, or some number that representssuch peaks, should be correlated to known concentrations of componentsthrough a calibration model before Raman spectrometry is used todetermine unknown concentrations. One method of obtaining numericalrepresentation of a peak of the Raman spectrum is by integrating thearea of the peak to obtain a single number that represents that peak.One may use a wavelength that is characteristic of a certain componentand integrate the area of the peaks at that wavelength to arrive at anumber representative for that component. The peaks, or area of thepeaks, or some other number representative of certain parts of the Ramanspectrum, must then be correlated to a known concentration using acalibration model, which may be based on assigning an area under acertain peak to a known concentration.

[0054] In a general procedure for developing a suitable calibrationmodel, a Raman spectrum is obtained for a sample of known concentrationof one component, or more preferably a mixture of components, that willbe the subject of analysis in the olefin polymerization process. Aplurality of separate regions of the spectrum are selected, based on theknown Raman spectra of the components. For example, there is a peak at16 to 20 wavenumbers that is characteristic of ethylene, so whereethylene will be one of the chemical components of interest, the regionof the spectrum at 1620 wavenumbers would likely be selected. Next, theareas of the selected regions are determined. A correlation is thenidentified between the area of the selected region and the concentrationof the component(s). By repeating this procedure for differentconcentrations and different components, and preferably by obtainingmultiple spectra and making multiple calculations for each concentrationand component, a calibration model may be obtained for the chemicalcomponents to be analyzed and monitored. A procedure for the developmentof a means within a computer for identifying substances using Ramanspectroscopy is disclosed in U.S. Pat. No. 4,620,284.

[0055] Certain peaks may be known to correspond to a particularcomponent, such as either the polyolefin product or the monomer.However, other peaks may correspond to more than one component or may beindistinguishable from each other although they correspond to differentcomponents. In such cases, obtaining a calibration model that candistinguish and correct quantify these components may seem impossible.It has been observed that such a calibration model is obtainable, thoughwith more difficulty than where the components have peaks that areseparate and readily distinguishable. Furthermore, it has beendiscovered that such a calibration model may be obtained and used evenwith low resolution Raman spectrometry equipment.

[0056] A calibration model is developed by measuring a sample using theRaman spectrometry equipment, and obtaining a Raman spectrum. Thespectrum, or the integrated area or intensity of the peaks of thatspectrum, are related to some value, preferably the concentration ofmonomer or other chemical component as measured by a gas chromatograph.For example, a Hewlett Packard 6890 with a flame ionization detector maybe employed, with a capillary column that is a 60 meter DB 1, 0.32 ID,column with a 1 micrometer film thickness. The gas chromatograph may beprogrammed to start at 40° C., hold for ten minutes, and then increasetemperature 12° C. per minute until it reached 275° C. The analysis timefor each sample should be approximately forty to forty-five minutes.

[0057] The concentrations determined by another analysis or by using aspecially made sample having a known concentration are correlated to theRaman spectrum or parts of the spectrum and used to develop acalibration model. The calibration model can then be used to determineor predict unknowns. A calibration model may be created usingcommercially available software, such as the GRAMS/32 and PLSplus/IQprograms available from Galactic Industries Corporation (Salem, N.H.).The calibration model may be calculated and future unknowns may bepredicted using the Galactic GRAMS/32 program. One may employ additionalstatistic or computational analysis to confirm or refine the correlationbetween chemical concentrations and the peaks generated by Ramanspectrometry analysis. For example, one may perform partial leastsquares regression analysis, using the Galactic PLSplus/IQ program.Partial least squares analysis enables the development of a calibrationmodel where one or more components may have some peaks that overlap. Acalibration model may predict the concentrations based on what is knownand assign concentrations to the unknowns.

[0058] Generally, suitable software must be capable of building modelsbetween spectral data and concentrations or other characteristicsdetermined some other method and which have a relationship to thespectral response. Such software is typical and commercially available.

[0059] In an example of the development of a calibration model, a RamanSystems R-2001C spectrometer was placed in a polyethylene pilot plantcontrol room, and an InPhotonics RP-785-100-01-SMA probe was placedabout 100 feet away in the settling leg product take-off line of apolyethylene reactor. A process gas chromatograph measured theconcentrations of ethylene, hexene and isobutane in the reactor flashgas. The spectra from the Raman Systems R-2001C unit and the GC analyzerdata were entered into the Grams/32 PLS-1 model to build the calibrationmodel.

[0060] The Grams/32 PLS-1 calibration file had the following parameters:Calibration Type: PLS-1, Diagnostic: Cross Validation, # Regions: 1(1750-0 cm⁻¹), # Samples: 34, # Points: 128.0, Maximum # Factors: 16, #Files Out: 1, Preprocessing: Mean Centering with Auto Baseline. Nosamples were excluded and no constituents were excluded. The recommendednumber of factors was 5. The actual versus predicted values for ethylenehad an R²=0.925 for the range 0 to 12 mol %. The actual versus predictedvalues for hexene had an R²=0.978 for the range 0 to 5.5 mol %. Theactual versus predicted values for isobutane had an R²=0.929 for therange 80 to 96 mol %.

[0061] By use of this model, we were able to predict ethylene and hexeneconcentrations within 11% of the GC analyzer value, which is anacceptable error range. With this level of accuracy, it is possible toeffectively monitor the concentration of ethylene and hexene in theliquid phase of the reactor.

[0062] Additionally, the present processes and apparatus may beautomated through the use of the computer 67, microprocessor,programmably logic controller or other suitable device to automaticallyadjust one or more conditions in response to the output signal from theRaman probe and/or the Raman analyzer.

[0063] Vibrations, movements, and shifting of the various Ramanspectrometry equipment can cause unexpected changes in the observedspectra. The types of errors induced are difficult to predict and maycause inaccuracies that result in limited precision. It is desirable toeliminate or minimize the effects of vibrations, movements, and shiftingin the Raman spectrometry equipment.

[0064] Sample probes may be placed at any location before, during and/orafter the olefin polymerization process, but it is generally advisableto place the Raman probe where it will provide information that isuseful for controlling the process and for providing analyticalinformation for calibration purposes. One preferable Raman probelocation in a polyolefin production process is near the point in theprocess where the polymerization reaction is near completion. Thisprovides analytical information regarding extent of reaction. Suchinformation allows for improved control of the polymerization process.

[0065] In the present methods and apparatus, there are two aspects withrespect to the placement of the Raman probe. In one aspect, the Ramanprobe is placed in the reactor such that it analyzes the slurry having aconcentration of solid polymer in a liquid containing diluent andreactants. The slurry may typically comprise 50 weight percent solids.The Raman probe is exposed to and measures polymer, diluent andreactants. It has been observed that the polyolefin particles tend todiffract or scatter the emitted light such that it is not observed bythe Raman probe. As a result, the presence of polyolefin particles maylower the signal intensity to about one-tenth of what it would be in aclear liquid. One problem with Raman spectrometry in a slurry is that asubstantial amount of scattered light does not come back to thedetector. One response to this problem has been to place the Raman probein the product removal area of the slurry loop polymerization process.

[0066] As another aspect, the Raman probe may be placed in a producttake-off line, where the polymer settles out from the slurry, therebyforming a clear liquid, and the probe is pointing into the clear liquid.The clear liquid may contain diluent such as isobutane and reactantssuch as ethylene and hexene. These separate from the solid polymer afterthe slurry leaves the reactor in the product take-off line or in thesettling leg. The polymer settles to the bottom and the clear liquid isabove the polymer. In the polymerization reactor, a valve opens so thatreaction slurry flows from the reactor into the product take-off line.After a suitable amount of polymer reaction slurry flows into theproduct take-off line, the valve closes and there is a certain dwelltime, such as about 30 seconds, during which the polyolefin is allowedto settle by gravity to the bottom of the settling leg. The Raman probemay be pointed in the top, which is the clear liquid. For a relativelyshort time, perhaps about three seconds, the Raman probe is exposed tothe slurry, but for a longer time, perhaps about 27 seconds, the probeis only exposed to the clear liquid because polyolefin settles outrapidly. It is advantageous to minimize the loss of scattered radiationcaused by the solid polyolefin particles.

[0067] It has been found that monitoring in the settling leg using Ramanspectrometry is better and quicker than monitoring at the flash tanksusing gas chromatography. The flash chamber is downstream from thesettling leg, and in the dual-stage flash system frequently used withloop reactors operating at pressures of about 600 psi, the reactionmixture is dropped from about 600 psi to about 300 psi in the firstflash chamber and then down to 15 psi in the second flash chamber. Thegas chromatograph in the first flash chamber takes about six minutes forits analysis and the gas chromatograph in the low pressure flash chambertakes about six minutes for its analysis. One must add those two timestogether, and so it takes 12 to about 15 minutes to complete the entiregas chromatographic analysis of the flash gas. Further, it isdisadvantageous to employ two numbers which are obtained at twodifferent pressures (for example, 300 psi and 15 psi) and it may lead tosome errors in the gas chromatographic method. In contrast, Ramananalysis of the clear liquid in the product take-off line is a fewseconds away from the reactor, and an analysis may be obtained morequickly.

[0068] An alternative process is the conversion of ethylene to 1-hexene.The reaction mixture in this process is itself a homogenous clearliquid, so the Raman probe may be used in the reactor without thenegative effects observed from solid polyolefin particles. In the1-hexene process, as well as other processes involving clear liquids,the Raman probe may be optimally placed in the reactor or in a samplingline.

[0069] Furthermore, it may be advantageous to develop a calibrationmodel for Raman spectrometry equipment to be used in a slurry olefinpolymerization process by calibrating in a 1-hexene process. Forexample, the Raman probe may be placed in the sampling line for the gaschromatograph system of a 1-hexene process. Then, data from the Ramansystem and the gas chromatograph system are obtained for the sameliquid. Those data may be used to correlate the Raman spectra toconcentrations determined by the gas chromatograph and develop acalibration model.

[0070] However, in a slurry polymerization process, the Raman probe mayalso be placed in the reactor where it is in contact with the slurry. Ithas been observed that there may be about a ten-fold reduction insignal, but some of the newer probes, such as from InPhotonics, arecapable of detecting the lower levels of scattered light from theslurry.

[0071] The ability to use low resolution Raman spectrometry systems issurprising, in that such systems are typically not capable of resolvingethylene peaks from hexene peaks. However, by the way the band shapeschange, base line resolution is not required, and modeling software canbe used to detect concentrations without resolving individual peaks. Inother words, it is not necessary to resolve the peaks corresponding toethylene and hexene in the present methods. This is similar to what isdone in near-infrared spectrometry, so that one uses partial leastsquare techniques to analyze those. The ability to use a low resolutionRaman spectrometer makes the present methods more economical. High cost,high resolution Raman spectrometry equipment generally have a resolutionof one to two wavenumbers and can resolve peaks that are only one or twowavenumbers apart. However, it has been discovered that such highresolution is not required for the present processes. A low resolutionRaman spectrometer having lower cost may be used. Its resolution may befrom about 15 wavenumbers to about 30 wavenumbers. As a result, the lowresolution Raman spectrometry equipment cannot resolve as many peaks asthe high resolution spectrometer, but it has been discovered that it isnot necessary to have one to two wavenumber resolution for monitoringconcentration of components in an olefin polymerization process. In thepreferred embodiments, the detector element is capable of discerningextremely low levels of radiation.

[0072] While the invention has been described in connection with one ormore embodiments, it will be understood that the invention is notlimited to those embodiments. On the contrary, the invention includesall alternatives, modifications, and equivalents as may be includedwithin the scope of the claims.

1. A process for olefin polymerization, comprising the acts of:contacting in a reaction mixture under slurry polymerization conditionsreactants comprising at least one olefin monomer with a heterogeneouscatalyst system comprising one or more catalytic metal compounds; makinga polyolefin; and monitoring the process by using Raman spectrometryequipment to provide an output signal representative of at least one ofthe reactants and the polyolefin.
 2. The olefin polymerization processof claim 1, wherein the output signal is representative of aconcentration of at least one of the reactants and the polyolefin. 3.The olefin polymerization process of claim 1, comprising the act ofadjusting the olefin polymerization process in response to the outputsignal provided by the Raman spectrometry equipment.
 4. The olefinpolymerization process of claim 1, wherein the olefin polymerizationprocess is adjusted by adjusting the concentration within the reactionmixture of at least one chemical component within the reaction mixture.5. The olefin polymerization process of claim 3, wherein the olefinpolymerization process is adjusted by adjusting one or morepolymerization conditions, wherein the polymerization conditionscomprise at least one of polymerization temperature, polymerizationpressure, withdrawal of the reaction mixture from the reactor, andcirculation rate of the reaction mixture within the reactor.
 6. Theolefin polymerization process of claim 1, wherein the Raman spectrometryequipment is operatively connected to a Raman fiber optic probe that isin contact with at least one of the reaction mixture and the polyolefin.7. The olefin polymerization process of claim 6, wherein the Raman fiberoptic probe comprises fused silica fiber optic cables within aprotective metal sheath.
 8. The polymerization process of claim 1wherein the Raman spectrometry equipment comprises low resolution Ramanequipment.
 9. The polymerization process of claim 8 wherein the Ramanlow resolution spectrometry equipment has a resolution in the range offrom about 15 wavenumbers to about 30 wavenumbers.
 10. The method ofclaim 1, wherein the at least one olefin monomer comprises ethylene. 11.The method of claim 10, wherein the reaction mixture comprises at leastone of a comonomer, hydrogen, and a co-catalyst.
 12. The method of claim11, wherein a comonomer is contacted with the ethylene, and thecomonomer comprises at least one of 1-butene, 1-pentene,4-methyl-1-pentene, and 1-hexene.
 13. The polymerization process ofclaim 1, wherein the reaction mixture is within a loop polymerizationreactor.
 14. The polymerization process of claim 13, wherein the act ofmonitoring by comprises the act of analyzing effluent from the looppolymerization reactor.
 15. The polymerization process of claim 1,wherein the olefin polymerization process is performed in two or morereactors connected in series, wherein effluent from an upstream reactoris provided as input to a downstream reactor, wherein the monitoringstep comprises the act of determining a concentration of the monomer inthe effluent by Raman spectrometry equipment, and the adjusting act ofcomprises the act of providing an amount of at least one of monomer andcomonomer in addition to the effluent to the downstream reactor.
 16. Amethod for monitoring and controlling an olefin polymerization reactioncomprising the acts of: contacting components of a reaction mixture in apolymerization reactor under polymerization conditions, the componentscomprising a monomer, a diluent, and a catalyst system; using Ramanspectrometry equipment to obtain a Raman spectrum; obtaining aconcentration of at least one of the components based upon the Ramanspectrum; and adjusting at least one polymerization condition inresponse to the concentration of the at least one of the components. 17.The method of claim 16, comprising the acts of: obtaining a Ramanspectrum of the reaction mixture; and determining the concentration ofat least one of the components through the use of a calibration model.18. The method of claim 17, comprising the act of developing thecalibration model using partial least squares analysis.
 19. The methodof claim 18, wherein the Raman spectrometry equipment is low resolutionRaman spectrometry equipment.
 20. The method of claim 19, wherein thelow resolution Raman spectrometry equipment has a resolution of about 15wavenumbers to about 30 wavenumbers.
 21. The method of claim 17,comprising the act of developing the calibration model for the Ramanspectrometry equipment to be used in the olefin polymerization reactionby calibrating in a process for converting ethylene to 1-hexene.
 22. Amethod of monitoring and controlling a polyolefin production process,comprising the acts of: exposing an in-situ polymerization mixture toradiation emission from a spectroscopic probe; acquiring a spectroscopicsignal from the in-situ mixture in substantially real-time in responseto the radiation emission via the spectroscopic probe; and analyzing thespectroscopic signal to determine at least one property of interest ofthe in-situ mixture, wherein the in-situ mixture comprises at least oneof a polyolefin, an olefin monomer, a comonomer, a diluent, a catalyst,a co-catalyst, and hydrogen.
 23. The method as recited in claim 22,wherein the spectroscopic probe comprises a Raman probe. 24 The methodas recited in claim 22, wherein the in-situ mixture comprises at leastone of a mixture in a reactor, a mixture fed to the reactor, a mixtureexiting the reactor, and a mixture exiting a flash vessel.
 25. Themethod as recited in claim 24, wherein the reactor comprises at leastone of a loop slurry reactor and a gas phase reactor.
 26. The method asrecited in claim 25, wherein the mixture exiting the flash vesselcomprises at least one of a flash gas exiting in the flash vesseloverhead and a substantially polyolefin stream exiting in the flashvessel bottom discharge.
 27. The method as recited in claim 22, whereinthe property of interest comprises a concentration in the in-situmixture of at least one of a monomer, a comonomer, a diluent, andhydrogen.
 28. The method as recited in claim 22, comprising at least oneof the acts of: adjusting at least one addition rate of a feed stream toa polymerization reactor in response to the property of interest;adjusting a concentration of at least one component in a feed stream toa polymerization reactor in response to the property of interest; andadjusting a concentration of at least one component in a polymerizationreactor in response to the property of interest.
 29. A method ofmonitoring and controlling a polyolefin production process, comprisingthe acts of: exposing a polyolefin polymerization mixture to a radiationemission from the Raman spectroscopic probe; acquiring a Ramanspectroscopic signal from the mixture in response to the radiationemission via the Raman spectroscopic probe; and analyzing thespectroscopic signal to determine at least one property of interest ofthe mixture, wherein the mixture comprises at least one of a polyolefin,an olefin monomer, a comonomer, a diluent, a catalyst, a co-catalyst,and hydrogen.
 30. The method as recited in claim 29, wherein the Ramanspectroscopic signal is acquired in substantially real-time, and themixture comprises an in-situ mixture in at least one of a polymerizationreactor feed stream, a polymerization reactor, a polymerization reactordischarge, a polymerization flash separator, and a polymerization flashseparator discharge.
 31. The method as recited in claim 29, wherein theproperty of interest comprises a concentration of at least one of asolid polyolefin, an olefin monomer, a comonomer, a diluent, andhydrogen.
 32. The method as recited in claim 29, wherein the mixturecomprises ethylene and hexene, and wherein low-resolution Raman is usedto determine the concentration of hexene in the mixture.
 33. The methodas recited in claim 29, wherein the mixture is an off-line samplecollected from at least one of a polymerization reactor feed stream, apolymerization reactor, a polymerization reactor discharge, apolymerization flash separator, and a polymerization flash separatordischarge.
 34. The method of claim 29, comprising the act of adjustingthe amount of at least one of a reactor feed component and a reactorcomponent, in response to the property of interest, wherein the reactorfeed component and reactor component comprise at least one of acatalyst, a co-catalyst, a monomer, a comonomer, a diluent, andhydrogen.
 35. A polyolefin production process, comprising: means forpolymerizing an olefin to a polyolefin; means for exposing an in-situpolymerization mixture to radiation emission from a Raman spectroscopicprobe; means for acquiring a Raman spectroscopic signal from the in-situmixture in substantially real-time in response to the radiation emissionvia the Raman spectroscopic probe; and means for analyzing the Ramanspectroscopic signal to determine at least one property of interest ofthe in-situ mixture, wherein the in-situ mixture comprises at least oneof a polyolefin, an olefin monomer, a comonomer, a diluent, a catalyst,a co-catalyst, and hydrogen.